Recension du dernier ouvrage de Derek Parfit, On What Matters.

« In this largest part of the book, Parfit attempts to demonstrate that the best versions of three prominent ethical theories traditionally viewed as being opposed to each other actually converge. The theories in question are consequentialism, Kantian deontology and contractualism. It is widely held, for example, that Immanuel Kant’s view rules out certain kinds of action no matter what their consequences. But if Parfit’s thesis is right, then a significant part of the history of Western moral philosophy has rested on a mistake.


Parfit painstakingly works his way through the most popular formulations of each view, revising them against counter-examples until they are each as tight as possible. The resulting theories are: a version of rule consequentialism according to which "everyone ought to follow the principles whose universal acceptance would make things go best"; a contractualist formulation of Kant’s categorical imperative, according to which "everyone ought to follow the principles whose universal acceptance everyone could rationally will"; and a revised account of Scanlon’s social contract theory, according to which "everyone ought to follow the principles that no one could reasonably reject".

Parfit argues that all three converge to prescribe the same set of actions, despite their emphases on features of morality that are in prima facie tension. He takes these actions to be recommended by a "triple theory" that combines three properties shared by all three of the aforementioned principles: "An act is wrong just when such acts are disallowed by the principles that are optimific, uniquely universally willable, and not reasonably rejectable."

Accordingly, he argues, rival theorists have been "climbing the same mountain on different sides" to reach the same view of what matters, namely "that we rich people give up some of our luxuries, ceasing to overheat the earth’s atmosphere, and taking care of this planet in other ways, so that it continues to support intelligent life". The triple theory, Parfit maintains, gives us overwhelming reasons to believe that this is the truth about what matters and then to act accordingly (with Parfit defending his claims about normative reasons and truths in the first and last parts of the book). »

On What Matters, Volumes I and II